MANIPULATING feed protein levels can reduce nitrogen excretion from grower and finisher pigs by 26% without losses in performance levels. A cut in nitrate levels could result.
This is the latest finding of a MAFF-funded study at ADAS Terrington Research Centre, Norfolk, which offered growers and finishers three diets with high, medium and low crude protein.
Pauline Lee ADAS pig nutritionist says: "Minimising nitrogen excretion, and hence nitrogen levels in slurry, could help to reduce nitrate leaching into water courses.
"In the study nitrogen excretion was reduced by a maximum of 39% in growers and 41% in finishing pigs using the low protein diet.
"But nitrogen retention was also reduced with the low protein diet which could affect lean deposition rates," says Dr Lee.
In growers and finishers retention was similar for both the high and medium protein diets. But, when fed the low protein diet growers retained 4g less nitrogen a day and finishers retained 13g a day less nitrogen, a large enough difference to reduce lean growth performance.
"Feed producers have the capability to manufacture a diet that would reduce nitrogen excretion by 26% now. But, they cannot yet produce a low protein diet that will maximise nitrogen retention and maintain the pigs condition.
To reduce nitrogen excretion by the pig it is necessary to supply amino acids in the diet more closely matched to the pigs dietary requirement.
Provisional results from a new programme of work, again funded by MAFF, have shown concentration of ammonia in rooms of pigs offered the low crude protein diet to be about a fifth of levels in those offered conventional diets.
ADAS pollution adviser Alan Brewer says: "Though the nitrate vulnerable zones have not yet been finalised and the integrated pollution prevention and control directive is still under discussion, experimental evidence that pollutants can be minimised at source is vital.
"First, because evidence can be used to reappraise the polluting value of a particular class of livestock. Second, because it shows the general public that the agricultural industry is acting responsibly in trying to protect the environment," says Mr Brewer.